I have three tabs open: Tab1, Tab2, and Tab3.
I'm on Tab2 and middle click on a link to open in a new tab (Tab4).
I go to Tab4 to read what was opened there.
With Tab4 still having focus, I close it.
At this point, how can I have focus return to Tab2 since it was most recent in Z order, not Tab3 as Firefox defaults to do?